EP0178034B1

EP0178034B1 - Process for preparing amorphous of intermetallic compounds by a chemical reaction

Info

Publication number: EP0178034B1
Application number: EP85301794A
Authority: EP
Inventors: Masao Komatsu; Hiroshi Fujita
Original assignee: Osaka University NUC
Current assignee: Osaka University NUC
Priority date: 1984-09-14
Filing date: 1985-03-14
Publication date: 1989-02-22
Also published as: JPH0250968B2; DE3568348D1; JPS6169931A; US4639363A; EP0178034A1

Description

The present invention relates to a process for preparing an amorphous phase of an intermetallic compound by a chemical reaction.
Amorphous metallic materials have come to prominence recently as new materials suitable for use in many fields of engineering because of their excellent physical and chemical properties.
For production of these amorphous metallic materials, two methods have been established, namely rapid cooling of liquid metal and vapor deposition of metal. Of these methods, the method of rapid cooling of liquid metal has become the most favoured recently and is able to produce an amorphous metal. In the method of vapor deposition of metal, the metal vapor which is produced by heating and dissolving the metal in vacuo is applied to a substrate maintained at the temperature of liquid helium or liquid nitrogen to obtain the amorphous metal.
The method of rapid cooling of liquid metal has the following problems: (1) the products are limited to ribbon or foil and it is impossible to amorphize a thick part of a particular required product, and (2) the field of use is narrowly limited because of the difficulty in controlling the rate of rapid cooling.
The method of vapor deposition is unable to produce a product thicker than that produced by the method of rapid cooling of liquid metal, and the product produced has a very high cost.
Additionally WO-A-8402926 discloses a method of forming amorphous phases in various alloys such as Zr₃ Rh by heating in pure hydrogen.
According to the present invention there is provided a process for preparing an amorphous phase of an intermetallic compound by a chemical reaction, characterised by heating an intermetallic compound of a Zr-Al alloy, at a temperature lower than the crystallisation temperature of the amorphous phase, in hydrogen-containing gas, thereby absorbing hydrogen and forming the amorphous phase.
AI is added to Zr, a single metal which generally forms a tightly bonded hydride, forming intermetallic compounds and then hydrogen is added to the compound to form an amorphous phase or phases.
It is possible to prepare sufficiently thick amorphous phases with the thickness being determined by selection of the conditions of H₂ gas absorption.
For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-

Figure 1 is a schematic view of an electric furnace suitable for carrying out the process of the present invention;
Figure 2 is a phase diagram of Zr-AI alloys suitable for use in the process of the present invention; and
Figure 3 is a sectional view of crystal structures of Zr-Al alloys photographed with an electron microscope before and after hydrogen absorption according to the process of the present invention.

Referring to Figure 1, crystals of intermetallic compounds 1 are treated by heating at given temperatures in a hydrogen-containing gas (pure H₂ gas, H₂ gas plus an inert gas such as Ar, etc.) in an electric furnace 3 having a heater 2. The heating temperature and the heating time are variable depending upon the type and properties of the intermetallic compounds, conditions for preparing the amorphous phases and the like. By the heat treatment, the crystals 1 absorb hydrogen, and the products produce turn to an amorphous phase by a chemical reaction between hydrogen, and the other atoms of the intermetallic compounds. In this case, the reaction accelerates with rising temperature and with a decreasing size of the crystals. The selection of the heating temperature is also important. The treatment temperature must be lower than the crystallization temperature of the amorphous phases.
Examples of conditions of the hydrogen absorption required to form the amorphous phases are as follows.
The thicknesses of the amorphous phases produced are freely controlled by controlling the hydrogen pressure of the surrounding gas, the temperature of hydrogen absorption and the time of hydrogen absorption.
The following examples are intended to illustrate this invention without limiting the scope thereof.

Example 1

30 at % of aluminium and 70 at % of sponge zirconium were subjected to arc welding to form a Zr-Al alloy. A phase diagram of the alloy is shown in Figure 2.
The alloy plate was then cut into thin films 0.2 mm thick with a discharge processing machine and electro-polished in a solution containing 9 parts of acetic acid and 1 part of perchloric acid to obtain a sample for viewing on an electron microscope. This sample was heat-treated at heating temperatures and heating times of 773K for 900 seconds (0.9 ks), 823K for 900 seconds (0.9 Ks) and 873K for 600 seconds (0.6 Ks), successively, in the electric furnace of Figure 1 having a surrounding gas at 0.1 MPa of AR+ 10% H₂ so as to absorb hydrogen. Each time the sample was subjected to the heat treatment at each heating temperature, the sample was cooled to the room temperature and observed within the same range of the electron microscope.
Figure 3 shows the results, Figure 3(a) is a photograph of the structure before hydrogen absorption. Figures 3(b), (c) and (d) are photographs of the structure after heat treatment under given conditions. In these photographs, crystal particles noted at A are Zr₂AI and the other parts are Zr₃AI. From these photographs, it can be seen that all the Zr₃AI changes to the amorphous phase with accelerating hydrogen absorption. By comparison of (c) and (d), it may be concluded that the reaction rate of Zr₃AI is faster than that of Zr₃Al.

Example 2

Zr-Al alloys (Zr-Zr₃Al and Zr₃AI-Zr₂AI) were electropolished to obtain samples in the same way described in the above Example 1. The obtained samples were heat-treated at heating temperatures in the range of from 470 to 873 K and heating times of in the range of from 900 to 1800 seconds (0.9 ks to 1.8 ks) in a surrounding gas containing H₂ at 0.1 MPa (1 atm). The samples were then cooled and observed within the same range of the electron microscope, respectively. The amorphization was recognized by observation of the sample changes due to the hydrogen absorption.

Summarizing the results of these Examples:

(1) By hydrogen absorption in Zr-Al alloys, amorphous phases are obtained and no stable hydrides are formed. (2) By repetition of hydrogen absorption, sufficient number and size amorphous phases are produced. (3) The amorphous phases of Zr₃AI are easier to obtain than those of Zr₂AI. (4) The amorphization proceeds from a thin edge of the sample, and preferentially at regions of lattice defects such as grain boundaries and dislocations. (5) Neither of the amorphous Zr-Al alloys crystallize by simple annealing in vacuo at temperatures higher than the temperatures of heat treatment under the hydrogen absorption.
Thus the size of the amorphous regions formed is controlled by controlling the hydrogen pressure, treatment temperature and time of treatment.
Using hydrogen absorption to change crystals into amorphous phases, amorphous products having a sufficient thickness (1 cm or more) can be produced by the selection of the conditions of hydrogen absorption. This is new because thick amorphous products cannot be obtained by conventional methods.
Thus the process of the present invention, has advantages such as:

(1) Possibility of thickness control of the amorphous regions by controlling the conditions of hydrogen absorption.
(2) Availability of amorphous phases of any form, including extremely complex forms prepared by other methods.
(3) Stability of the amorphous phases over a wide range of temperatures.
(4) Preparation of finely ground amorphous powder by grinding the obtained amorphous materials.
(5) Preparation of finely ground powder from which hydrogen is released by heating the amorphous materials at temperatures higher than the temperature of crystallization.
(6) Repeated use of the amorphous materials as the alloys of hydrogen absorption from which hydrogen is released at a given temperature by using the nature of the amorphous materials being constant temperatures of crystallization.

Consequently, the process of the present invention may have the following uses:

(1) Preparation of amorphous materials having sufficient thicknesses.
(2) Amorphization of surface phases or whole phases having complex forms obtained by other means.
(3) Preparation of a superfine ground powder.
(4) Hydrogen absorption using the solid from which hydrogen is released at a given temperature.

Claims

1. A process for preparing an amorphous phase of an intermetallic compound by a chemical reaction, characterised by heating an intermetallic compound of a Zr-Al alloy, at a temperature lower than the crystallisation temperature of the amorphous phase, in hydrogen-containing gas, thereby absorbing hydrogen and forming the amorphous phase.

2. A process according to claim 1, in which the size of the amorphous regions formed is controlled by controlling the hydrogen pressure, treatment temperature and time of treatment.

3. A process according to claim 1, in which the Zr-Al alloy treated is Zr₃AI and the hydrogen absorption is carried out at a temperature in the range of from 350 to 650 K for 900 seconds at a pressure of 0.1 Megapascals (1 atmosphere).

4. A process according to claim 1, in which the Zr-Al alloy treated is Zr₂AI, and the hydrogen absorption is carried out at a temperature in the range of from 400 to 700 K for 1,800 seconds at a pressure of 0.1 Megapascals (1 atmosphere).

5. A process according to claim 1 or claim 2, in which the Zr-Al alloy treated is Zr-Zr₃AI or Zr₃Al-Zr₂Al, and the hydrogen absorption is carried out at a temperature in the range of from 470 to 873 K for a time in the range of from 900 to 1,800 seconds at a pressure of 0.1 Megapascals (1 atmosphere).